iommu/amd: Treat per-device exclusion ranges as r/w unity-mapped regions

Some buggy BIOSes might define multiple exclusion ranges of the
IVMD entries which are associated with the same IOMMU hardware.
This leads to the overwritten exclusion range (exclusion_start
and exclusion_length members) in set_device_exclusion_range().

Here is a real case:
When attaching two Broadcom RAID controllers to a server, the first
one reports the failure during booting (the disks connecting to the
RAID controller cannot be detected).

This patch prevents the issue by treating per-device exclusion
ranges as r/w unity-mapped regions.

Discussion:
  * https://lists.linuxfoundation.org/pipermail/iommu/2019-November/040140.htmlSuggested-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd_iommu_init.c

@@ -71,6 +71,8 @@
 #define IVHD_FLAG_ISOC_EN_MASK          0x08
 
 #define IVMD_FLAG_EXCL_RANGE            0x08
+#define IVMD_FLAG_IW                    0x04
+#define IVMD_FLAG_IR                    0x02
 #define IVMD_FLAG_UNITY_MAP             0x01
 
 #define ACPI_DEVFLAG_INITPASS           0x01
@@ -1121,16 +1123,14 @@ static void __init set_device_exclusion_range(u16 devid, struct ivmd_header *m)
 	if (!(m->flags & IVMD_FLAG_EXCL_RANGE))
 		return;
 
-	if (iommu) {
 	/*
-		 * We only can configure exclusion ranges per IOMMU, not
-		 * per device. But we can enable the exclusion range per
-		 * device. This is done here
+	 * Treat per-device exclusion ranges as r/w unity-mapped regions
+	 * since some buggy BIOSes might lead to the overwritten exclusion
+	 * range (exclusion_start and exclusion_length members). This
+	 * happens when there are multiple exclusion ranges (IVMD entries)
+	 * defined in ACPI table.
 	 */
-		set_dev_entry_bit(devid, DEV_ENTRY_EX);
-		iommu->exclusion_start = m->range_start;
-		iommu->exclusion_length = m->range_length;
-	}
+	m->flags = (IVMD_FLAG_IW | IVMD_FLAG_IR | IVMD_FLAG_UNITY_MAP);
 }
 
 /*